Generally, a gas fuel container used for a portable gas burner is filled with liquefied gas. The liquefied gas is sprayed out of the fuel container by internal gas pressure regularly maintained in the gas fuel container.
However, the internal gas pressure may be increased at a high temperature, causing an inadvertent accident such as the deformation and explosion of the fuel container. For example, when the fuel container is exposed to, for example, the heat of summer, since the internal pressure of the fuel container is excessively increased, an inadvertent accident such as the explosion of the container may be incurred. Furthermore, when cooking is performed with a pot having a bottom wider than the portable gas burner, excessive radiant heat spreads out along the bottom of the pot to reach the gas fuel container. As a result, a temperature of the fuel container is increased to increase the internal pressure of the fuel container, resulting in the explosion of the container.
FIGS. 1 to 3 show a conventional gas fuel container.
As shown in the drawings, a conventional gas fuel container 100 includes a main body 99 and a mounting cap 101 mounted on a top of the main body 99. The mounting cap 101 is provided at a central portion with a projected coupling portion 102 in which a valve stem 103 and a housing 104 are coupled. A spring 105 being disposed in the housing 104 elastically supports the valve stem 103 upward. An opening/closing seal 106 is disposed between a top of the housing 104 and the coupling portion 102 of the mounting cap 101.
A gas spraying hole 107 is defined by an upper-inner cavity of the valve stem 103. A concave portion 108 is formed on an outer circumference of the valve stem 103. An orifice 109 is formed through the concave portion 108 of the valve stem 103. The inner circumference of the opening/closing seal 106 is tightly fitted around the concave portion 108 so that the orifice 109 can be selectively opened and closed in response to external force to exhaust the internal gas.
A predetermined level of internal pressure regularly acts in the gas fuel container to spray the gas to an external side. However, when the internal pressure is increased by the external heat, an inadvertent accident may be incurred due to a risk such as the deformation and explosion of the container.
Therefore, to prevent such an accident there is provided a conventional safety apparatus against excessive internal pressure as shown in FIG. 4.
As shown in the drawing, a housing 202 is coupled to a center of a mounting cap 201 and a valve stem 203 is installed in the housing 202. An over pressure safety spring 204 and a supporting spring 205 are disposed in the housing 202 to elastically support the valve stem 203. Disposed on a hook step 202a of the housing 202 is an opening/closing seal 202a on which a spring seat 207 is disposed.
The opening/closing seal 206 is tightly fitted around a concave portion 203a of the valve stem 203 to selectively open an orifice 208 formed through the valve stem 203. The spring seat 207 is fitted around the valve stem 203 and is biased by the over pressure safety spring 204 to allow the opening/closing seal 206 to tightly contact the hook step 202a. 
In the above-described safety apparatus, in order to exhaust or fill gas out of or in the container 200, when external force is applied to push down the valve stem 203 as shown in FIG. 5, the supporting spring 205 is compressed and the orifice 208 blocked by the opening/closing seal 206 is opened, thereby allowing the gas to be exhausted out of or filled in the container 200.
Meanwhile, when the internal pressure of the container 200 is increased to be higher than the elastic force of the over pressure safety spring 204, as shown in FIG. 6, the over pressure safety spring 204 is compressed and the valve stem 203 is moved upward. As a result the opening/closing seal 206 is separated firm the hook step 202a to define a gas exhaust path. The gas forming the excessive internal pressure is exhausted through the gas exhaust path and an inner cavity of the housing 202, thereby lowering the internal pressure to prevent the explosion of the container 200.
However, since the above-described safety apparatus is designed such that the gas is introduced into the container only through the orifice 208 in the course of filling the gas into the container (an opposite direction of the arrow in FIG. 5), the filling efficiency is deteriorated as compared with a filling structure of a conventional fuel container shown in FIG. 3.
Meanwhile, as shown in FIG. 5, when the gas spray pressure is increased above a predetermined level (6 kgf/cm2 for a butane gas container) in use, a governor is operated to cut off the spray of the gas and to separate the container 200 from the gas burner. In this state, when the internal pressure of the container 200 is increased above a predetermined level (14 kgf/cm2 for a butane gas container), the valve stem 203 is moved upward (see FIG. 6) to reduce the internal pressure.
However, when the container 200 is maintained without being separated from the gas burner due to, for example, the malfunction of the governor, since the valve stem 203 cannot be moved upward, the opening/closing seal 206 maintain closely to contact the hook step 202a. As a result, the internal over pressure gas cannot be exhausted, causing the container 200 to be exploded.
In addition, the safety apparatus is designed such that the internal over pressure gas is exhausted by moving the valve stem 203 installed in the housing 202, an overall length of the valve stem 203 and the housing 202 is increased by the moving distance, thereby increasing the costs of the assembling parts.